4.1 Genetic Variability and Natural Selection

In the next chapter, I show how scenario visualization fi ts into the evolutionary

psychologist’s schematization of the mind to form a more complete

picture of how it is that humans evolved the ability to solve

vision-related problems creatively. In this chapter, I trace the evolution of

the visual system beginning with organisms that developed a light/dark

sensitivity area and culminating in the complex activities involved in an

aspect of conscious cognitive visual processing that I call scenario visualization.

I do this utilizing the anatomical evidence from fossils and living

species thought to be homologous to ancient species. I also use evidence

from ancient toolmaking techniques because, in my estimation, the evolution

of tool types parallels the evolution from noncognitive visual processing,

through cognitive visual processing, to scenario visualization, a form

of conscious cognitive visual processing (also see Arp, 2006, 2007a, 2008c).

The variety and complexity of tools discovered and dated by archeologists

offer compelling evidence that the brain and visual system have evolved

with the passage of time. Before tracing the evolution of the visual system,

I fi rst must say something about the general evolutionary principles of

genetic variability and natural selection.

As was noted in the last section of the previous chapter, neural development

is dependent upon genetic and environmental factors. Even though

neurulation follows a genetic blueprint, the way in which neurons differentiate,

localize, and ultimately perform depends upon the internal chemiconeural

environment of nervous system processes as well as the interaction

between the nervous system and the external environment. This neurobiological

process is representative of the general evolutionary pattern that all

processes of organisms follow. The evolutionary pattern consists of genetic variability and the natural selection of traits that are most fi t given a particular

environment.

Darwin’s (1859) insights concerning evolution—ones that still hold

today—are the following: (1) there is variation in organisms such that they

differ from each other in ways that are inherited; (2) there is a struggle or

competition for existence, since more organisms are born than can survive;

(3) there is a natural selection of the traits that are most fi t given a particular

environment; (4) organisms fortunate enough to have the variation in

traits that fi t a particular environment will have an increased chance of

surviving to pass those traits on to their progeny; and (5) natural selection

leads to the accumulation of favored variants, which may produce new

species or a segregated gene pool, given the right environmental conditions

and a certain amount of time.

Since Darwin’s time, we have been able to determine that a major source

of variation in organisms has to do with genetic mutation. A gene is a

functional segment of DNA located at a particular site on a chromosome

in the nucleus of all cells. Basically, DNA is the template from which RNA

copies are made that transmits genetic information concerning an organism’s

physical and behavioral traits (phenotypic traits) to synthesis sites in

the cytoplasm of the cell. RNA takes this information to ribosomes in a

cell where amino acids, and then proteins, are formed according to that

information. The proteins are the so-called building blocks of life, since they

ultimately determine the physical characteristics of organisms (Carroll,

2005; Audesirk et al., 2002; Strickberger, 1985, 2000; Dawkins, 1986; Mayr,

2001; Ruse, 2000; also see the relevant papers in Arp & Rosenberg, 2008;

Arp & Ayala, 2008).

DNA and RNA are composed of nucleic acids. These nucleic acids specify

the amino-acid sequences of all the proteins needed to make up the physical

characteristics of an organism, much like a code or cryptogram. This

code consists of specifi c sequences of nucleotides that are composed of a

sugar (deoxyribose in DNA, ribose in RNA), a phosphate group, and one

of four different nitrogen-containing bases, namely, adenine, guanine,

cytosine, and thymine in DNA (uracil replaces thymine in RNA). These

four bases are like a four-letter alphabet, and triplets of bases form threeletter

words or codons that identify an amino acid or signal a function.

There are 64 possible permutations of the four bases, and if one of the

nucleotides in a sequence is either deleted or substituted, or if an alternate

nucleotide is inserted, then a mutation is said to occur. A mutation is

nothing other than an alteration in the nucleotide sequence of a DNA or

RNA molecule. Mutations can result from a variety of environmental

The Evolution of the Visual System and Scenario Visualization 93

sources, including certain chemicals, radiation from X rays, and ultraviolet

rays in sunlight. Mutations also can occur spontaneously. However, the

most common source of mutations occurs regularly in base pairing during

replication, as a cell prepares for cell division. In other words, mutations

are occurring all of the time, since cell division is occurring in organisms

all of the time.

Now, the genetic makeup of an organism directly affects its phenotypic

characteristics. Whether an animal will have all of its limbs, or be stronger

than another member of its species, or look more appealing to the opposite

sex—all of these phenotypic characteristics are under genetic control

(Carroll, 2005; Strickberger, 1985, 2000; Mayr, 2001; Lewontin, 1992). The

examples of the manipulations of HOX genes that result in monstrous

animal forms I spoke about in the last section of the previous chapter

should make this point clear.

When an organism exists in a particular environment, the chance of it

being naturally selected to survive depends upon whether its genetic

makeup happened to have produced the phenotypic characteristics necessary

for optimal survival in that particular environment. To a certain

extent, the randomness of a mutation makes the business of life a “crapshoot.”

If your wolf genes coded you to have three legs instead of four,

then it is likely you will not survive in the wolf pack out in the forests of

Colorado. And if your rabbit genes coded you to have poor eyesight, then

it is likely you will not survive in the same forests of Colorado, where your

eyesight is essential for avoiding such packs of wolves. The phenotypic

effects of mutations need only be slight so that, for example, one wolf may

be just a little stronger, or a little faster, or a little more aggressive than

the rest of the pack. This small genotypic variation leads to a slight phenotypic

benefi t, giving the wolf an advantage in hunting, mating, and

passing its genes on to future generations.

Natural selection is a mechanism of evolution by which the environment

favors the reproductive success of individuals possessing desirable genetic

variants with greater phenotypic fi tness, increasing the chance that those

genotypes for the phenotypic traits will predominate in succeeding generations.

The evolutionary principles of genetic variation and the natural

selection of the traits most fi t in a particular environment are illustrated

in fi gure 4.1. This illustration owes its genesis to productive conversations

with my graduate school colleague at Saint Louis University, Kevin Decker,

as well as with biologists such as Robert Wood, at Saint Louis University,

and Charles Granger, at the University of Missouri—St. Louis. In this fi gure,

I try to show how natural selection acts like a sieve that allows for a certain phenotypic characteristic to pass through to a subsequent generation. The

various shapes represent organisms having certain phenotypic traits that

are genetically controlled. The sieves themselves (the rectangular planes)

represent the certain environments in which these organisms live. The

preformed slot or hole represents the optimal survival of organisms possessing

a desirable phenotypic trait in that particular environment.

The point of this illustration is to represent pictorially what biologists

such as Audesirk et al. (2002) and Berra (1990) have claimed about genetic

variability and natural selection. According to Audesirk et al. (2002, p. 175):

“Mutations are essential for evolution, because these random changes in

DNA sequence are the ultimate source of all genetic variation. New base

Figure 4.1

The evolutionary sieve

Generic Variants

Environment A:

The square was

most fit of all the

generic variants.

Environment B:

The rhombus was

most fit of all the

generic variants.

Environment C:

The triangle was

most fit of all the

generic variants.

sequences undergo natural selection as organisms compete to survive and

reproduce. Occasionally, a mutation proves benefi cial in the organism’s

interactions with its environment. The mutant base sequence may spread

throughout the population and become common as organisms that possess

it outcompete rivals that bear the original, unmutated base sequence.” In

Berra’s (1990, p. 8) words: “Some genetic variants will be better adapted to

their environment than others of their sort, and will therefore tend to

survive to maturity and to leave more offspring than will organisms with

less favorable variations. . . . The environment is the selecting agent, and

because the environment changes over time and from one region to

another, different variants will be selected under different environmental

conditions.”

Stated simply, the various species around us today are those organisms

that have made it through one of these environmental sieves, the result

of some fortunate mutation in combination with the traits that were most

fi t for some environment. As we will see, the human nervous system

and human creative problem solving arose by the same evolutionary

mechanisms.

In the next chapter, I show how scenario visualization fi ts into the evolutionary

psychologist’s schematization of the mind to form a more complete

picture of how it is that humans evolved the ability to solve

vision-related problems creatively. In this chapter, I trace the evolution of

the visual system beginning with organisms that developed a light/dark

sensitivity area and culminating in the complex activities involved in an

aspect of conscious cognitive visual processing that I call scenario visualization.

I do this utilizing the anatomical evidence from fossils and living

species thought to be homologous to ancient species. I also use evidence

from ancient toolmaking techniques because, in my estimation, the evolution

of tool types parallels the evolution from noncognitive visual processing,

through cognitive visual processing, to scenario visualization, a form

of conscious cognitive visual processing (also see Arp, 2006, 2007a, 2008c).

The variety and complexity of tools discovered and dated by archeologists

offer compelling evidence that the brain and visual system have evolved

with the passage of time. Before tracing the evolution of the visual system,

I fi rst must say something about the general evolutionary principles of

genetic variability and natural selection.

As was noted in the last section of the previous chapter, neural development

is dependent upon genetic and environmental factors. Even though

neurulation follows a genetic blueprint, the way in which neurons differentiate,

localize, and ultimately perform depends upon the internal chemiconeural

environment of nervous system processes as well as the interaction

between the nervous system and the external environment. This neurobiological

process is representative of the general evolutionary pattern that all

processes of organisms follow. The evolutionary pattern consists of genetic variability and the natural selection of traits that are most fi t given a particular

environment.

Darwin’s (1859) insights concerning evolution—ones that still hold

today—are the following: (1) there is variation in organisms such that they

differ from each other in ways that are inherited; (2) there is a struggle or

competition for existence, since more organisms are born than can survive;

(3) there is a natural selection of the traits that are most fi t given a particular

environment; (4) organisms fortunate enough to have the variation in

traits that fi t a particular environment will have an increased chance of

surviving to pass those traits on to their progeny; and (5) natural selection

leads to the accumulation of favored variants, which may produce new

species or a segregated gene pool, given the right environmental conditions

and a certain amount of time.

Since Darwin’s time, we have been able to determine that a major source

of variation in organisms has to do with genetic mutation. A gene is a

functional segment of DNA located at a particular site on a chromosome

in the nucleus of all cells. Basically, DNA is the template from which RNA

copies are made that transmits genetic information concerning an organism’s

physical and behavioral traits (phenotypic traits) to synthesis sites in

the cytoplasm of the cell. RNA takes this information to ribosomes in a

cell where amino acids, and then proteins, are formed according to that

information. The proteins are the so-called building blocks of life, since they

ultimately determine the physical characteristics of organisms (Carroll,

2005; Audesirk et al., 2002; Strickberger, 1985, 2000; Dawkins, 1986; Mayr,

2001; Ruse, 2000; also see the relevant papers in Arp & Rosenberg, 2008;

Arp & Ayala, 2008).

DNA and RNA are composed of nucleic acids. These nucleic acids specify

the amino-acid sequences of all the proteins needed to make up the physical

characteristics of an organism, much like a code or cryptogram. This

code consists of specifi c sequences of nucleotides that are composed of a

sugar (deoxyribose in DNA, ribose in RNA), a phosphate group, and one

of four different nitrogen-containing bases, namely, adenine, guanine,

cytosine, and thymine in DNA (uracil replaces thymine in RNA). These

four bases are like a four-letter alphabet, and triplets of bases form threeletter

words or codons that identify an amino acid or signal a function.

There are 64 possible permutations of the four bases, and if one of the

nucleotides in a sequence is either deleted or substituted, or if an alternate

nucleotide is inserted, then a mutation is said to occur. A mutation is

nothing other than an alteration in the nucleotide sequence of a DNA or

RNA molecule. Mutations can result from a variety of environmental

The Evolution of the Visual System and Scenario Visualization 93

sources, including certain chemicals, radiation from X rays, and ultraviolet

rays in sunlight. Mutations also can occur spontaneously. However, the

most common source of mutations occurs regularly in base pairing during

replication, as a cell prepares for cell division. In other words, mutations

are occurring all of the time, since cell division is occurring in organisms

all of the time.

Now, the genetic makeup of an organism directly affects its phenotypic

characteristics. Whether an animal will have all of its limbs, or be stronger

than another member of its species, or look more appealing to the opposite

sex—all of these phenotypic characteristics are under genetic control

(Carroll, 2005; Strickberger, 1985, 2000; Mayr, 2001; Lewontin, 1992). The

examples of the manipulations of HOX genes that result in monstrous

animal forms I spoke about in the last section of the previous chapter

should make this point clear.

When an organism exists in a particular environment, the chance of it

being naturally selected to survive depends upon whether its genetic

makeup happened to have produced the phenotypic characteristics necessary

for optimal survival in that particular environment. To a certain

extent, the randomness of a mutation makes the business of life a “crapshoot.”

If your wolf genes coded you to have three legs instead of four,

then it is likely you will not survive in the wolf pack out in the forests of

Colorado. And if your rabbit genes coded you to have poor eyesight, then

it is likely you will not survive in the same forests of Colorado, where your

eyesight is essential for avoiding such packs of wolves. The phenotypic

effects of mutations need only be slight so that, for example, one wolf may

be just a little stronger, or a little faster, or a little more aggressive than

the rest of the pack. This small genotypic variation leads to a slight phenotypic

benefi t, giving the wolf an advantage in hunting, mating, and

passing its genes on to future generations.

Natural selection is a mechanism of evolution by which the environment

favors the reproductive success of individuals possessing desirable genetic

variants with greater phenotypic fi tness, increasing the chance that those

genotypes for the phenotypic traits will predominate in succeeding generations.

The evolutionary principles of genetic variation and the natural

selection of the traits most fi t in a particular environment are illustrated

in fi gure 4.1. This illustration owes its genesis to productive conversations

with my graduate school colleague at Saint Louis University, Kevin Decker,

as well as with biologists such as Robert Wood, at Saint Louis University,

and Charles Granger, at the University of Missouri—St. Louis. In this fi gure,

I try to show how natural selection acts like a sieve that allows for a certain phenotypic characteristic to pass through to a subsequent generation. The

various shapes represent organisms having certain phenotypic traits that

are genetically controlled. The sieves themselves (the rectangular planes)

represent the certain environments in which these organisms live. The

preformed slot or hole represents the optimal survival of organisms possessing

a desirable phenotypic trait in that particular environment.

The point of this illustration is to represent pictorially what biologists

such as Audesirk et al. (2002) and Berra (1990) have claimed about genetic

variability and natural selection. According to Audesirk et al. (2002, p. 175):

“Mutations are essential for evolution, because these random changes in

DNA sequence are the ultimate source of all genetic variation. New base

Figure 4.1

The evolutionary sieve

Generic Variants

Environment A:

The square was

most fit of all the

generic variants.

Environment B:

The rhombus was

most fit of all the

generic variants.

Environment C:

The triangle was

most fit of all the

generic variants.

sequences undergo natural selection as organisms compete to survive and

reproduce. Occasionally, a mutation proves benefi cial in the organism’s

interactions with its environment. The mutant base sequence may spread

throughout the population and become common as organisms that possess

it outcompete rivals that bear the original, unmutated base sequence.” In

Berra’s (1990, p. 8) words: “Some genetic variants will be better adapted to

their environment than others of their sort, and will therefore tend to

survive to maturity and to leave more offspring than will organisms with

less favorable variations. . . . The environment is the selecting agent, and

because the environment changes over time and from one region to

another, different variants will be selected under different environmental

conditions.”

Stated simply, the various species around us today are those organisms

that have made it through one of these environmental sieves, the result

of some fortunate mutation in combination with the traits that were most

fi t for some environment. As we will see, the human nervous system

and human creative problem solving arose by the same evolutionary

mechanisms.